PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       readonly — set the readonly attribute for variables

SYNOPSIS

       readonly name[=word]...

       readonly -p

DESCRIPTION

       The  variables  whose  names are specified shall be given the readonly attribute. The values of variables
       with the readonly attribute cannot be changed by subsequent assignment, nor can those variables be  unset
       by  the  unset  utility.  If the name of a variable is followed by =word, then the value of that variable
       shall be set to word.

       The readonly special built-in shall support the Base Definitions volume of  POSIX.1‐2017,  Section  12.2,
       Utility Syntax Guidelines.

       When  -p  is  specified,  readonly  writes  to  the standard output the names and values of all read-only
       variables, in the following format:

           "readonly %s=%s\n", <name>, <value>

       if name is set, and

           "readonly %s\n", <name>

       if name is unset.

       The shell shall format the output, including the proper use of  quoting,  so  that  it  is  suitable  for
       reinput  to the shell as commands that achieve the same value and readonly attribute-setting results in a
       shell execution environment in which:

        1. Variables with values at the time they were output do not have the readonly attribute set.

        2. Variables that were unset at the time they were output do not have a value at the time at  which  the
           saved output is reinput to the shell.

       When no arguments are given, the results are unspecified.

OPTIONS

       See the DESCRIPTION.

OPERANDS

       See the DESCRIPTION.

STDIN

       Not used.

INPUT FILES

       None.

ENVIRONMENT VARIABLES

       None.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       See the DESCRIPTION.

STDERR

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

        0    All name operands were successfully marked readonly.

       >0    At  least  one  name  could  not  be  marked  readonly, or the -p option was specified and an error
             occurred.

CONSEQUENCES OF ERRORS

       Default.

       The following sections are informative.

APPLICATION USAGE

       None.

EXAMPLES

       readonly HOME PWD

RATIONALE

       Some historical shells preserve the readonly  attribute  across  separate  invocations.  This  volume  of
       POSIX.1‐2017 allows this behavior, but does not require it.

       The  -p  option allows portable access to the values that can be saved and then later restored using, for
       example, a dot script. Also see the RATIONALE for export for a description  of  the  no-argument  and  -p
       output cases and a related example.

       Read-only  functions  were  considered,  but  they  were  omitted  as  not  being  historical practice or
       particularly useful. Furthermore,  functions  must  not  be  read-only  across  invocations  to  preclude
       ``spoofing''  (spoofing  is  the  term for the practice of creating a program that acts like a well-known
       utility with the intent of subverting the real intent of the user) of administrative or security-relevant
       (or security-conscious) shell scripts.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Section 2.14, Special Built-In Utilities

       The Base Definitions volume of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                      READONLY(1POSIX)